Keratin fibers including human hair may be colored (dyed) by the oxidative condensation reaction of a dyeing composition, particularly oxidative dyeing composition. In general, as described in Korean Patent Publication No. 10-0757028 or the like, such a dyeing composition comprises a first part containing an oxidative dye precursor, coupler and an alkaline agent, and a second part containing an oxidizing agent, and the two parts are mixed with each other upon use.
The oxidative dye precursor and coupler infiltrate into hair and are coupled with each other via oxidative condensation, resulting in color formation. During such color formation, the alkaline agent (e.g. ammonia) contained in the first part accelerates the formation of perhydroxy anions of the oxidizing agent (e.g. hydrogen peroxide), and the perhydroxy anions cause the oxidation of a dye and melanin decomposition, resulting in color formation and decoloration.
However, although the perhydroxy anions of the oxidizing agent serve to carry out the oxidation of a dye and melanin decomposition, the oxidative agent molecules may react among themselves as undesired side reaction to form radicals, which, in turn, may cause decomposition of hair proteins, leading to hair damages, comprising degradation of hair gloss and color formability. In addition, ammonia is used typically as an alkaline agent contained in the first part to accelerate the oxidation. However, such an alkaline agent having volatility is problematic in that it causes generation of a pungent smell. Further, such an alkaline agent increases pH, thereby causing scalp irritation and eye-smarting.
To solve the above-mentioned problems, many approaches have been suggested. For example, Korean Patent Laid-Open No. 10-2005-0074860 discloses a method for enhancing color formability by using a phosphate surfactant capable of forming a multi-lamella liquid crystal structure and inducing a delay in reaction between the oxidative dye precursor and the coupler. However, the method suggests no solution to the problems of a pungent smell caused by the alkaline agent and sulfur compounds as well as eye-smarting.
Referring to the above-mentioned pungent smell and eye-smarting, when an alkaline agent present in an aqueous phase (continuous phase) is allowed to be in an inner phase of micelles, vesicles or emulsion, or when the emulsion is provided with very high viscosity, it is possible to reduce a pungent smell and eye-smarting.
However, in the case of a W/O formulation having an aqueous phase (continuous phase) as an inner phase of micelles, a dye co-existing with the aqueous phase is present in the inner phase at the same time, thereby making it difficult to carry out mass transfer (adhesion) to the hair, resulting in degradability of color formability. In addition, when the emulsion has very high viscosity, it cannot be applied to the hair with ease and the mass transfer is also difficult in this case, resulting in degradation of color formability.